Process for the alkylation of aromatic hydrocarbons

ABSTRACT

Process for the alkylation of aromatic hydrocarbons by reaction of an olefin with an aromatic hydrocarbon in the presence of a complex catalyst comprising a metal halide and aromatic hydrocarbons, which comprises measuring the activity of the catalyst by determination of the ratio of the meta dialkylated derivatives to the sum of ortho and para disubstituted derivatives and adding fresh metal halide in such amounts that said ratio is maintained at predetermined values.

Messina et al.

[451 Dec. 24, I974 PROCESS FOR THE ALKYLATION OF AROMATIC HYDROCARBONSInventors: Giuseppe Messina, Alghero; Loreno Lorenzoni, Porto Torres;Natale Bertolini, Milan, all of Italy Societa Italiana ResineS.I.R.S.p.A., Milan, Italy Filed: Nov. 15, 1973 Appl. No.: 416,138

Assignee:

Foreign Application Priority Data Nov. 30, 1972 Italy 32270/72 U.S. Cl260/671 C, 260/671 R, 260/671 P Int. Cl C07c 3/56 Field of Search260/671 R, 671 C, 671 P References Cited UNITED STATES PATENTS 10/1966Bodre 260/671 R McMinn 260/671 R Roberts 260/671 R Primary ExaminerC.Davis Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak[57] ABSTRACT Process for the alkylation of aromatic hydrocarbons byreaction of an olefin with an aromatic hydrocarbon in the presence of acomplex catalyst comprising a metal halide and aromatic hydrocarbons,which comprises measuring the activity of the catalyst by determinationof the ratio of the meta dialkylated derivatives to the sum of ortho andpara disubstituted derivatives and adding fresh metal halide in suchamounts that said ratio is maintained at predetermined values.

3 Claims, 4 Drawing Figures PATENTEU 3.856378 sum um R2 Figlb PROCESSFUR THE ALKYLATION F AROMATIC HYDROCARBONS The present invention relatesto an improved process for the alkylation of an aromatic hydrocarbon inthe presence of a complex Friedel-Crafts catalyst. More particularly,the invention relates to a method for the continuous determination andchecking of the activity of the complex organometal halide catalyst,i.e. a complex comprising a metal halide and aromatic compounds duringthe alkylation of an aromatic hydrocarbon with an olefin.

The invention will be specifically described with reference to thesynthesis of ethylbenzene by alkylation of benzene with ethylene in thepresence of a complex aluminium trichloride catalyst and activators suchas hydrochloric acid or ethyl chloride.

DESCRIPTION or THE PRIOR ART The reaction of an alkylating agent, suchas an olefin or an alkyl halide, with aromatic compounds in the presenceof a metal halide is well known and widely used in industry.

It is known that the active catalyst in this reaction is not the solidmetal halide, but a complex comprising the metal halide and aromaticcompounds.

This substance, which iscommonly referred to as a complex catalyst,resembles a heavy oil and has a variable composition depending on thesubstances present in the reacting system.

For example, in the production of ethylbenzene by alkylation of benzenewith ethylene, the complex cata lyst comprises the metal halide togetherwith benzene, ethylbenzene, and polyethylbe'nzenes.

Under the usual working conditions, an aromatic hydrocarbon and anolefin are allowed to react in the presence of a complex aluminiumtrichloride catalyst to produce a liquid alkylation product.

In the preparation of ethylbenzene, the contact between the complexcatalyst and the liquid alkylation mixture is ensured by the ethylenebubbling into the system as well as by mechanical agitators.

The complex catalyst is then easily separated from the liquid alkylationproduct by passage of the reaction mixture into a decanter.

The separation of the heavier phase consisting of the complex catalystfrom the lighter phase consisting of the liquid alkylation product takesplace in the decanter.

The complex catalyst is then recycled to the alkylation reactor.

It is known that the complex catalyst is poisoned by substances such aswater, sulphur compounds, polynuclear aromatic compounds, etc.

For example, though commercial benzene is main tained at a relativelyhigh purity and is dehydrated by azeotropic distillation, traces ofmoisture and other impurities are always present and destroy theactivity of the catalyst.

A similar effect is caused by the heavy polyalkylated aromatic compoundsformed as by-products in the alkylation reaction.

The complex catalyst thus loses its activity in a certain time, and asatisfactory level of catalytic activity is maintained in practice bycontinuous removal of a portion of the circulating complex catalyst,addition of fresh aluminium trichloride, and recycling of the catalystactivated in this way.

In the past, no methods were known for the measurement of the activityof the complex catalyst, and the additions of fresh aluminiumtrichloride were carried out quite empirically on the basis of theexperience of the staff employed to operate the plant. Therefore, toensure that the reaction did not come to a stop, quantities of freshcatalyst greater than those required were added.

To overcome this disadvantage, a number of techniques have recently beendeveloped for the measurement of the activity of the complex catalyst,so that the addition of the aluminium trichloride can be carried out ina motivated and reasonable manner.

For example, the activity can be checked by measurement of the viscosityof the complex catalyst or by means of the fluorescence phenomena of thealkylation product.

SUMMARY It has now been found, in accordance with the present invention,that the activity of a complex Friedel- Crafts catalyst used in thealkylation of an aromatic hydrocarbon with an olefin can be determineddirectly by determination of the concentrations, or preferably theratios of the concentrations, of the dialkyl derivatives formed asbyproducts in the alkylation reaction itself.

One object of the present invention is therefore a simple and sensitivemethod for the determination of the activity of an alkylation catalystwhen an aromatic hydrocarbon is being alkylated with an olefin in thepresence of a complex organo-metal halide catalyst.

Another object of the present invention is a method for continuous andaccurate checking that allows the maintenance of the activity of acomplex organo-metal halide catalyst in the alkylation reaction.

A further object of the present invention is a method for thedetermination of the activity of a complex organometal halide catalystin the alkylation of an aromatic hydrocarbon with an olefin that allowsthe maintenance of a constantly high output of the alkylated product.

It is known that the disubstituted compounds are formed during thealkylation by further reaction of the monoalkylated products and bytransalkylation phenomena, and that the extent of their formation iscontrolled by kinetic and thermodynamic factors.

The present invention is essentially based on the discovery that in analkylation system in which fresh catalyst is not added the ratio of thequantity of the meta isomer to the sum of the quantities of the orthoand para dialkyl isomers decreases regularly with time both in thealkylation product and in the complex catalyst and finally shows asudden decrease corresponding to the termination of the reaction.

For example, when ethylene is allowed to react with benzene in the usualmolar ratios in the presence of three parts by volume of complexcatalyst per part of alkylation mixture and without the addition offresh aluminium trichloride, it is known that the ratio of metadiethylbenzene to the sum of the ortho and para isomers decreasescontinuously with time and undergoes a rapid drop corresponding to thedeactivation of the catalyst.

In accordance with the process of the present invention, the activity ofthe complex Friedel-Crafts catalyst used in the alkylation of anaromatic hydrocarbon with an olefin is maintained at a high level bymeasurement of the ratio of the meta dialkyl derivative to the sum ofthe ortho and para isomers and addition of the metal halide in aquantity sufficient to maintain a predetermined value of the said ratio.

The advantages of such a procedure are numerous.

Thus by operation in the manner described, it is possible to checkcontinuously the activity of the complex catalyst and hence to add onlythe quantity of metal halide necessary to maintain the desired activity.

It is also possible to carry out the alkylation with catalyst activitiesclose to the termination activity with complete safety of operation,with the result that the maximum use is made of the catalyst and aconsiderable economic advantage is thus obtained.

It is also possible to automate fully the metal halide feed withmechanisms controlled by the apparatus used for the measurement of theactivity of the catalyst.

Finally, the risk of termination of the reaction as a result ofpoisoning of the catalyst due to accidental introduction of deactivatingsubstances into the reaction medium is avoided.

In comparison with the methods formerly used, the present inventionfirst of all has the advantage that it allows easy and accuratemeasurement of the activity of the catalyst.

Moreover, it involves the measurement of values controlled bythermodynamic and kinetic parameters, and hence valid for all catalyticsystems of the Friedel- Crafts type. Such measurements are also validwhen the deactivation results from the accidental introduction ofpoisoning substances, such as carbon monoxide, acetylene, hydrogensulphide, water, sulphur dioxide, mercaptans, etc., into the system.

The measurement of the ratio of the meta dialkylation product to the sumof the ortho and para isomers can be carried out by various analyticaltechniques such as the infrared technique and gas-liquid chromatography.

Accurate measurements of the said ratio are possible by the infraredtechnique.

However, the preferred system for the determination of the ratio isgas-liquid chromatography. It is extremely easy to effect the separationof the aromatic dialkylation products by means of chromatographiccolumns of various types, particularly columns with a partition liquidhaving low polarities. In this case the meta isomer separates from theother isomers, which give a single peak.

In the determination of the ratio of the dialkylated aromaticderivatives, therefore, one need only measure the areas of thecorresponding peaks and then determine the ratio of the values of thesaid areas.

This can be carried out by a normal process chromatograph coupled withan integrator and a ratio measurer.

It is clear, moreover, that once theupper and lower limits of the ratioof the dialkylation products have been established for the operatingconditions used, an automatic system can be designed for the metering ofthe fresh catalyst.

In other words, the aluminium trichloride feed can be controlledautomatically. by the instrument that measures the activity of thecomplex catalyst.

The measurement of the activity of the complex catalyst may be carriedout on samples taken at the outlet from the industrial alkylationreactors, but for better control, it is preferable to use a system thatcarries out such measurements both at the inlet to and at the outletfrom the reactors.

It is not advisable to carry out the measurement only at the outlet fromthe reactor, since this would not allow the detection of poisoning ofthe complex catalyst due to the introduction of contaminating substanceswith the reactants.

The above-mentioned measurements find application throughout the rangeof activity of the complex Friedel-Crafts catalyst; it is preferable inevery case to carry out the alkylation in a range of values not very farfrom that in which deactivation of the catalyst occurs, in order to makethe maximum use of the catalyst itself.

Thus in the case of the alkylation of benzene with ethylene, thepreferred range is that in which the weight ratio of the metadiethylbenzene to the sum of the ortho and para isomers assumes valuesof from 1.5:] to 2.1:1 in the alkylation product or from 1.8:] to 2.3:1in the complex catalyst.

Outside these values, one has either catalysts that are unnecessarilyactive or catalyst whose activities are too close to the terminationactivity or completely inactive catalysts.

The minimum and maximum values indicated for the ratio of thedialkylated isomers are indicative values, since variations are possibleaccording to the operating conditions such as temperature, pressure,contact time, ratio of the reactants, and purity of the reactantsthemselves.

The alkylation of the aromatic compounds with olefins may be carried outin the most diverse ways while still remaining within the scope of thepresent invention.

The alkylation reaction may be carried out in any type of reactorsuitable for the purpose, either continuously or discontinuously.

The apparatus and the technique used in the alkylation process are wellknown and do not form part of the present invention.

The reaction is generally carried out by introduction of the preformedcomplex catalyst, the benzene, the hydrochloric acid, and the ethylene,in the case of the formation of ethylbenzene, into the reaction zoneheld at a temperature of about 60 to 150C.

The preferred temperatures vary from to 90C in particular when thereaction is carried out at ambient pressure. The higher temperatures arenormally chosen when the pressure used during the alkylation is aboveatmospheric pressure.

Still in the production of ethylbenzene, one normally uses a quantity ofcomplex catalyst of from I to 3 parts by weight per part by weight ofalkylation mixture while the weight ratio'of benzene to ethylene ismaintained in the range from 4:1 to 7:1.

The quantity of halohydric acid, generally hydrochloric acid, normallyused as a promotor of the alkylation reaction, may vary from I part byweight per 1000 parts by weight of ethylene to 1 part by weight per 10parts by weight of ethylene.

After the magnetic stirrer of the reactor and the pump for the recyclingof the complex catalyst have been started up, the temperature of thereactor is brought to 83 to 85C by means of the oil circulation. Thefollowing are then fed to the reactor: hydrochloric acid at a rate of0.5 grams/hour, the mixture of benzene "hour. The other conditions withthe reaction proceeding are: rate of recycling of the complex catalyst1500 grams/hour and weight ratio of complex catalyst to alkylationproduct 3:1.

Samples of the complex catalyst and of the alkylation product areremoved at regular intervals. These samples are analysed to determinethe ratio of the meta diethylbenzene to the sum of the ortho and paraisomers.

It has thus been possible to correlate the variation of these ratioswith the aging of the catalyst and the yield of ethylbenzene. I

The experimental data found are shown in Table 1 and in the attachedFIGS. 1 and 2.

More particularly, the time in hours is given in the table under A, theweight ratio of meta diethylbenzene to the sum of the ortho and paraisomers in the complex catalyst under B, the same ratio in thealkylation prodnot under C, and the yield of ethylbenzene expressed asthe percentage by weight of ethylbenzenein the alkylation product underD.

FIG. 11 shows the variation,.with time, of the ethylbenzene yield and ofthe weight ratio of meta diethylbenzene to the sum of the ortho and paraisomers found in the complex catalyst.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLE 1 The apparatus used consists of A glass reactor with a capacityof 350 ml, fitted with an oil-circulation thermostat andan'electromagnetic stirrer.

A glass decanter connected to the reactor, with a capacity of 750 ml,for the separation of the liquid alkylation product (light phase) fromthe complex catalyst (heavy phase).

Three glass columns packed with Raschig rings, connected in series. Thecomplex catalyst (coming from the decanter) is fed into the top of thefirst of said columns in such a way as to strip any ethylene notconverted in the reactor. The complex catalyst then flows into thealkylation reactor. The liquid mixture of benzene and polyethylbenzenesis fed into the top of the second column in such a way as to strip thehydrochloric acid that has escaped from the first column. This liquidmixture also flows in the alkylation reactor. In the third column, anyacid not solubilized in the preceding columns is stripped with water.

Two metering pumps, the first for recycling of the complex catalyst andthe second for charging of the mixture of benzene and polyethylbenzenes.

Means for feeding ethylene and hydrochlorid acid to the alkylationreactor.

750 grams of complex catalyst and 250 grams of akylation product from anearlier reaction for the preparation of ethylbenzene from ethylene andbenzene are introduced into the apparatus.

The catalyst was prepared from alkylation product, aluminiumtrichloride, and hydrochloric acid.

Table l-Continued A B C D The same variation is shown in FIG. 2 and thesaid ratio is determined in the alkylation product. In the figures, thetime in hours is plotted on the abscissa, while the values of the yieldof ethylbenzene (R and of the ratio of the diethyl derivatives (R areplotted on the ordinate.

EXAMPLE 2 A liquid complex aluminium trichloride catalyst is prepared byreaction of metallic aluminium and hydrochloric acid in the presence ofa hydrocarbon alkylation product formed in the alkylation reaction ofbenzene with ethylene and having the following composition: ethylbenzene47%, benzene 40%, polyethylbenzenes 13% by weight.

The procedure described in Example 1 is then followed, and the resultsare shown in FIG. 3.

In particular, the weight ratio of meta diethylbenzene to the sum of theortho and para isomers found in the complex catalyst is shown in FIG. 3.

In this figure R and R have the same meaning as in FIGS. 1 and 2.

EXAMPLE 3 The operation is carried out under the conditions of Example1, exhausting the complex catalyst from an earlier alkylation and thenactivating it by addition of fresh aluminium trichloride.

The course is shown in FIG. 4, in which the time in hours is plotted onthe abscissa and the value of the weight ratio (R of meta diethylbenzeneto the sum of the ortho and para isomers found in the complex catalyston the ordinate.

What we claim is:

11. A process for the alkylation of aromatic hydrocarbons by reaction ofan olefin with an aromatic hydrocarbon in the presence of a complexcatalyst comprising a metal halide and aromatic hydrocarbons, in whichthe activity of the complex catalyst is maintained by addition of freshmetal halide, characterized in that the activity of the catalyst ismeasured by determination of the ratio of the meta dialkylated productsto the sum of pared.

3. A process according to claim 1, characterized in that ethylene andbenzene are reacted in the presence of a complex catalyst containingaluminium chloride to give ethylbenzene and polyethylbenzenes.

1. A PROCESS FOR THE ALKYLATION OF ARMOATIC HYDROCARBONS BY REACTION OFAN OLEFIN WITH AN AROMATIC HYDROCARBON IN THE PRESENCE OF A COMPLEXCATALYST COMPRISING A METAL HALIDE AND AROMATIC HYDROCARBONS, IN WHICHTHE ACTIVITY OF THE COMPLEX CATALYST IS MAINTAINED BY ADDITION OF FRESHMETAL HALIDE, CHARACTERIZED IN THAT THE ACTIVITY OF THE CATALYST ISMEASURED BY THE SUM OF ORTHO AND PARA DIALKYLATED DERIVATIVES IN THECOMPLEX CATALYST OR IN THE LIQUID ALKYLATION PRODUCT AND FRESH PLEXHALIDE IS ADDED TO THE COMPLEX CATALYST IN SUCH AMOUNTS METAL HALIDE ISADDED TO THE COMPLEX CATALYST IN SUCH AMOUNTS AS TO MAINTAIN SAID RATIOAT PREDETERMINED VALUES.
 2. A process according to claim 1,characterized in that monoalkylated aromatic hydrocarbons are prepared.3. A process according to claim 1, characterized in that ethylene andbenzene are reacted in the presence of a complex catalyst containingaluminium chloride to give ethylbenzene and polyethylbenzenes.